Turbine engines are used as the primary power source for many types of aircrafts. The engines are also auxiliary power sources that drive air compressors, hydraulic pumps, and industrial gas turbine (IGT) power generation. Further, the power from turbine engines is used for stationary power supplies such as backup electrical generators for hospitals and the like.
Most turbine engines generally follow the same basic power generation procedure. Compressed air generated by axial and/or radial compressors is mixed with fuel and burned, and the expanding hot combustion gases are directed against stationary turbine vanes in the engine. The vanes turn the high velocity gas flow partially sideways to impinge on the turbine blades mounted on a rotatable turbine disk. The force of the impinging gas causes the turbine disk to spin at high speed. Jet propulsion engines use the power created by the rotating turbine disk to draw more air into the engine and the high velocity combustion gas is passed out of the gas turbine aft end to create forward thrust. Other engines use this power to turn one or more propellers, fans, electrical generators, or other devices.
Fan, low, and high pressure compressor (LPC/HPC) components are primary components in the cold section for any turbine engine and typically include complex shapes. Bladed discs (“Blisks”) for example have airfoils, or blades, with surface curvature that extends in three dimensions. Blisk is the term used in the aeronautical field for a unitary piece with a rotor and airfoils. A blisk, for example, contains a series of airfoils that radiate out from a central hub. Blisks are being increasingly specified in modern turbine engine design as a method to achieve high compression in relatively short lateral spaces. These components are typically fabricated and repaired by joining separately formed blades to a disc or hub. It is desirable to optimize the design of these components during the build process. In addition, the fan/LPC/HPC components may be subject to stress loadings during turbine engine operation, and may also be impacted by foreign objects such as sand, dirt, and other such debris. Accordingly, the fan/LPC/HPC components can degrade over time due to wear, erosion and foreign object impact. Sometimes LPC/HPC components are degraded to a point at which they must be repaired or replaced, which that result in significant operating expense and time out of service.
There are several traditional methods for fabricating and repairing worn turbine engine components such as blisks, and each method has some limitations in terms of success. For example, friction welding can be used to join the blades to the disc or hub. Friction welding is achieved by moving either one or both of the blades and disc relative to one another with sufficient force to generate frictional heat, thereby joining the blade to the disc. Many times a stub is formed upstanding about a periphery of the disc for attachment of the blade. The joining stub typically follows the axial curve of the disc or hub and includes a joining surface that also follows the axial curve of the disc or hub. In other instances, friction welding is used to join the blades to the disc by providing a slot that follows the axial contour of the disk as adjoining surface.
The geometry of turbine engine blisks makes them particularly vulnerable to inadequate joining of the blades and disc due to insufficient stiffness that is achieved during the above-described welding processes. Accordingly, it is often important to establish and/or verify the structural integrity thereof. Loss of structural integrity in an object can be caused by material defects.
Non-Destructive Evaluation (NDE) methods refer to a class of methods that can be used to inspect objects for defects. NDE methods are often used to inspect materials for defects, such as structural anomalies, inclusions, cracks, etc. However, many conventional NDE methods often provide incomplete or otherwise inadequate inspections. This is especially true in difficult geometries, such as in the friction welded blisks noted above.
It would therefore be desirable to provide improved NDE methods for use with friction welded blisks to detect material defects therein. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.